Imaging apparatus and processing method thereof

ABSTRACT

A solid-state imaging apparatus of a dynamic range enlarged by reading out a carrier accumulated in a carrier accumulation unit at a plurality of times during a single carrier accumulation time period.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging apparatus and the processingmethod thereof.

2. Description of the Related Arts

The following three kinds of driving methods for enlarging a dynamicrange of a solid-state imaging apparatus is disclosed in Japanese PatentApplication Laid-Open No. 2005-328493. The first kind is such that acarrier overflowed from a photo receiving unit is accumulated infloating diffusion and an added capacitor so as to be turned into adynamic range expansion signal. The second kind is such that, during apart of the period only within the accumulation period of the photoreceiving unit, the overflowed carrier is accumulated so as to be turnedinto a dynamic range expansion signal. The third kind is such that thesignal accumulated in the photo receiving unit as well as the dynamicrange expansion signal are added inside a pixel so as to be output.

Japanese Patent Application Laid-Open No. 2005-328493 discloses that thefloating diffusion contains a dark impurity region and a PN junctioncomposed of a p-type well, and that a photo diode is an embedded photodiode. However, there is a problem that the floating diffusion is greatin dark output due to the generation current in a depletion layer forthe photo diode.

Although there is no cause for concern when the accumulation period isshort, when the accumulation period is long, a problem occurs that manysignals are generated due to dark currents of a floating diffusionregion that accumulates the dynamic range expansion signals as well asthe added capacitor. This is because the FD and CS units are not the PNjunction capacitor of the berried type, and as a result, the darkcurrent is increased, and therefore, they are not suitable as holdingunits for holding the carrier for a long time. The signal amplitude atthe FD (or a vertical signal line) is put on restrictions by a darkcurrent component, and no signal amplitude for the dynamic rangeexpansion signal can be secured.

This problem can be improved to a certain degree by the second kind ofthe driving method by making the accumulation period of the dynamicrange expansion signal short. However, this time, the accumulationperiod of the photo diode and the accumulation period of the dynamicrange expansion signal are deviated from each other, and therefore,there arises a major problem that the synchronicity of the two signalsare harmed. Whichever case it may be, in the case of moving image, sincethe accumulation period is short, no problem is caused, whereas in thecase of the still image photographing such as a digital single-lensreflex camera, it is a major problem.

An object of the present invention is to provide an imaging apparatusand its processing method capable of enlarging a dynamic range, whilesecuring synchronicity of the carrier accumulation period of aphotoelectric conversion unit and a carrier accumulation unit.

SUMMARY OF THE INVENTION

An imaging apparatus of the present invention includes: a photoelectricconversion unit for generating a carrier by a photoelectric conversionand for accumulating the carrier generated; a carrier accumulation unitfor accumulating the carrier overflowed from the photoelectricconversion unit; a read out unit for reading out, at plural times, asignal based on the carrier accumulated in the carrier accumulation unitduring a single carrier accumulation period for the carrier generated bythe photoelectric conversion unit; and a reset switch for resetting thecarrier accumulated in the carrier accumulation unit after each readingby the read out unit.

The processing method of the imaging apparatus of the present inventionis a processing method of the imaging apparatus including: aphotoelectric conversion unit for generating a carrier by photoelectricconversion and for accumulating the carrier generated, and a carrieraccumulation unit for accumulating the carrier overflowed from thephotoelectric conversion unit, wherein the method includes steps of:reading out, at plural times, a signal based on the carrier accumulatedin the carrier accumulation unit in a single carrier accumulation periodfor the carrier generated by the photoelectric conversion unit and aresetting the carrier accumulated in the carrier accumulation unit aftereach reading.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a configuration example of a pixelunit inside a photo receiving unit according to a first embodiment ofthe present invention.

FIG. 2 is a block diagram showing a configuration example of asolid-state imaging apparatus according the first embodiment of thepresent invention.

FIG. 3 is a timing chart showing a drive timing in a pixel unit of a(n+2)th row from a n-th row of a photo receiving region.

FIG. 4 is a view showing photoelectric conversion characteristics of thefirst embodiment.

FIG. 5 is a timing chart showing a drive timing of the solid-stateimaging apparatus according to a second embodiment of the presentinvention.

FIG. 6 is a circuit diagram showing a configuration example of the pixelunit inside the photo receiving region according to the secondembodiment.

FIG. 7 is a view showing photoelectric conversion characteristics of thesecond embodiment.

FIG. 8 is a view showing a configuration example of a camera system in acase when the solid-state imaging apparatus according to a fourthembodiment of the present invention is used for a camera.

FIG. 9 is a timing chart showing a drive timing of the solid-stateimaging apparatus according to a fifth embodiment of the presentinvention.

FIG. 10 is a timing chart showing a drive timing of the solid-stateimaging apparatus.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

By using FIGS. 1 to 4, a first embodiment of the present invention willbe described.

FIG. 2 is a block diagram showing a configuration example of a MOS typesolid-state imaging apparatus according to the first embodiment of thepresent invention, and FIG. 1 is a circuit diagram showing aconfiguration example of a pixel unit inside a photo receiving region101 of FIG. 2. This pixel unit is two-dimensionally plurally disposedinside the photo receiving region 101.

In FIG. 1, reference symbol PD denotes a photo diode. The photo diode PDconverts a received light into a carrier and accumulates it. Referencesymbol TX denotes a transfer switch. Reference symbol RES denotes areset switch for resetting a floating diffusion region FD. Referencesymbol SF denotes an input MOS electric field effect transistor of asource follower taking the floating diffusion region FD as an inputterminal. Reference symbol SEL denotes a row selection switch. ReferenceFD denotes a source follower input terminal, and denotes a floatingdiffusion region, which holds a transferred carrier, and converts itinto voltage. Reference symbol SW denotes a switch for controlling theconnection of a holding capacitor Ccs and the floating diffusion regionFD. Reference symbol Ccs is a holding capacitor for accumulating thecarrier overflowed from the photo diode PD. In addition to the photodiode PD, by providing the holding capacitor Ccs, the carrieraccumulation capacitance can be increased, and the dynamic range can beexpanded. The driving method of this pixel unit will be described laterwith reference to FIG. 3.

In FIG. 2, reference numeral 100 denotes a sensor chip. Numeral 101denotes a light receiving region. Numerals 102 a and 102 b denote columnsignal processing circuits. Numerals 103 a and 103 b denote horizontalscanning circuits. Numeral 104 denotes a vertical scanning circuit.Numerals 105 a and 105 b denote a read out amplifier. Numerals 106 a and106 b denote a common signal line unit. Numerals 107 a and 107 b denoteoutput line unit.

The photo receiving region 101 has a plurality of pixel units of FIG. 1,and generates two-dimensional pixel signals. The vertical scanningcircuit 104 sequentially selects the row of the pixel unit of the photoreceiving region 101, and the signal of the pixel unit of the selectedrow is read out to the column signal processing circuits 102 a and 102b. The horizontal scanning circuits 103 a and 103 b sequentially selectthe columns of the signals of the column signal processing circuits 102a and 102 b, and allow the selected signals to be output to the read outamplifiers 105 a and 105 b through the common signal line units 106 aand 106 b. The read out amplifiers 105 a and 105 b amplify the signals,and output them to the outside through the output line units 107 a and107 b.

FIG. 3 is a timing chart showing a drive timing in the pixel unit of an(n+2)th from an n-th row of the photo receiving region 101. Hereinafter,a processing method of the solid-state imaging apparatus will bedescribed. Each pulse is a signal generated by the vertical scanningcircuit 104, and is as follows. ΦRES denotes the gate drive pulse of areset transistor RES of FIG. 1. ΦTX denotes the gate drive pulse of atransfer transistor TX of FIG. 1. ΦSW denotes the gate drive pulse of aswitch transistor SW of FIG. 1. ΦSEL denotes the gate drive pulse of atransistor SEL of FIG. 1. The (n to n+2) at the end of each pulsedenotes a row. Further, the vertical scanning circuit 104 outputs a highlevel to the gate of the switch SEL so as to enable the switch SEL toturn on, and outputs a low level to the gate of the switch SEL so as toenable the switch SEL to turn off.

A transfer switch TX, when the signal ΦTX becomes a high level,transfers the signal accumulated in the photo diode PD to the floatingdiffusion region FD which is an input terminal of the source flowertransistor SF. The reset switch RES, when the signal ΦRES becomes a highlevel, resets the floating diffusion region FD. The holding capacitorCcs is a capacitor for holding the carrier overflowed from the photodiode PD. The switch SW is a switch for controlling the connection withthe floating diffusion region FD and the holding capacitor Ccs. Theswitch SEL is a switch for selecting the row of the pixel unit of thephoto receiving region 101, and reads out the output signal of thesource flower transistor SF to the column signal processing circuit 103aor 103 b when the gate becomes a high level.

As shown in FIG. 3, the dynamic range expansion signal of the photodiode PD is read out by dividing it in four times. The operations of theperiods T1 to T15 will be described below.

The period T1 is a period in which the reset operation of the photodiode PD of the n-th row is performed. The period T1 is a period inwhich the high level state of the pulse is maintained, and specifically,it is a period in which the signals ΦTX_n, ΦRES_n, and ΦSW_n maintainthe high level, and the other signals in the figure maintain the lowlevel. The transistors TX, RES, and SW of the n-th row are turned on,and the photo diode PD and the holding capacitor Ccs of the n-th row arereset.

The period T2 is a reset period of the photo diode PD of the (n+1)throw. Specifically, it is a period in which the signals ΦTX_n+1,ΦRES_n+1, and ΦSW_n+1 maintain the high level, and the other signals inthe figure maintain the low level. The transistors TX, RES, and SW ofthe (n+1)th row are turned on, and the photo diode PD and the holdingcapacitor Ccs of the (n+1)th row are reset.

The period T3 is a reset period of the photo diode PD of the (n+2)throw. Specifically, it is a period in which the signals ΦTX_n+2,ΦRES_n+2, and ΦSW_n+2 maintain the high level, and the other signals inthe figure maintain the low level. The transistors TX, RES, and SW ofthe (n+2)th row are turned on, and the photo diode PD and the holdingcapacitor Ccs of the (n+2)th row are reset.

The period T4 is a first read out period of the dynamic range expansionsignal of the n-th row. The signal ΦSW_n becomes the low level from thehigh level. The transistor SW of the n-th row is turned off from turningon. The holding capacitor Ccs accumulates the carrier overflowed fromthe photo diode PD, and as long as the transistor SW is turned on, itscarrier is output to the floating diffusion region FD through thetransistor SW. By making the signal ΦSEL_n a high level from a lowlevel, the source follower transistor SF reads out the signal based onthe potential of the floating diffusion region FD as the dynamic rangeexpansion signal. The column signal processing circuit 102 a or 102 breads out the dynamic range expansion signal and holds it.

Next, the signal ΦRES_n becomes a high level, and the transistor RES ofthe n-th row is turned on. As a result, the floating diffusion region FDof the n-th row is reset.

The period T5 is a first read out period of the reset signal of the n-throw. The signal ΦRES_n becomes a low level, and the transistor RES ofthe nth-row is turned off. By making the signal ΦSEL_n a high level froma low level, the source follower transistor SF reads out the signalbased on the potential of the floating diffusion region FD as a resetsignal (noise signal). The column signal processing circuit 102 a or 102b reads out the reset signal and holds it. The read out amplifier 105 aor 105 b subtracts the reset signal from the dynamic range expansionsignal, so that the pixel signal reduced in noise is output.

The period T6 is a first reset period of the dynamic expansion signal ofthe n-th row. The signals ΦRES_n and ΦSW_n become a high level and thetransistors RES and SW of the n-th row are turned on. As a result, theholding capacitor Ccs of the n-th row is reset.

The period T7 is a first read out period of the dynamic range expansionsignal of the (n+1)th row. The signal ΦSW_n+1 becomes a low level from ahigh level. The transistor SW of the (n+1)th row is turned off fromturning on. The holding capacitor Ccs accumulates the carrier overflowedfrom the photo diode PD, and as long as the transistor SW is turned on,outputs its carrier to the floating diffusion region FD through thetransistor SW. By making the signal ΦSEL_n a high level from a lowlevel, the source follower transistor SF reads out the signal based onthe potential of the floating diffusion region FD as a dynamic rangeexpansion signal. The column signal processing circuit 102 a or 102 breads out the dynamic range expansion signal and holds it.

Next, the signal ΦRES_n+1 becomes a high level, and the transistor RESof the (n+1)th row is turned on. As a result, the floating diffusionregion FD of the (n+1)th row is reset.

The period T8 is a first read out period of the dynamic expansion signalof the (n+1)th row. The signal ΦRES_n+1 becomes a low level, and thetransistor RES of the (n+1)th row is turned off. By making the signalΦSEL_n a high level from a low level, the source follower transistor SFreads out the signal based on the potential of the floating diffusionregion FD as a reset signal (noise signal). The column signal processingcircuit 102 a or 102 b reads out the reset signal and holds it. The readout amplifier 105 a or 105 b subtracts the reset signal from the dynamicrange expansion signal, so that the pixel signal reduced in noise isoutput.

The period T9 is a first reset period of the dynamic range expansionsignal of the (n+1)th row. The signals ΦRES_n+1 and ΦSW_n+1 become ahigh level, and the transistors RES and SW of the (n+1)th row are turnedon. As a result, the holding capacitor Ccs of the (n+1)th row is reset.

Even in the (n+2)th row, the processings of the first read out period ofthe dynamic range expansion signal of the (n+2)th row, the first readout period of the reset signal of the (n+2)th row, and the first restperiod of the dynamic range expansion signal of the (n+2)th row areperformed. These processings are the same as the processings of theperiods T4, T5, and T6 of the n-th row described above.

Next, similarly to the periods T4, T5, and T6, the processings of asecond read out period of the dynamic range expansion signal of the n-throw, a second read out period of the reset signal of the n-th row, and asecond reset period of the dynamic range expansion signal of the n-throw are performed. Further, after that, similarly, the processings of athird read out period of the dynamic range expansion signal of the n-throw, a third read out period of the reset signal of the n-th row, and athird reset period of the dynamic range expansion signal of the n-th roware performed.

Further, similarly to the periods T7, T8, and T9, the processings of thesecond read out period of the dynamic range expansion signal of the(n+1)th row, the second read out period of the reset signal of the(n+1)th row, and the second reset period of the dynamic range expansionsignal of the (n+1)th row are performed. Further, after that, similarly,the processings of the third read out period of the dynamic rangeexpansion signal of the (n+1)th row, the third read out period of thereset signal of the (n+1)th row, and the third reset period of thedynamic range expansion signal of the (n+1)th row are performed.

Further, similarly to the periods T4, T5, and T6, the processings of thesecond read out period of the dynamic range expansion signal of the(n+2)th row, the second read out period of the reset signal of the(n+2)th row, and the second reset period of the dynamic range expansionsignal of the (n+2)th row are performed. Further, after that, similarly,the processings of the third read out period of the dynamic rangeexpansion signal of the (n+2)th row, the third read out period of thereset signal of the (n+2)th row, and the third reset period of thedynamic range expansion signal of the (n+2)th row are performed.

The period T10, similarly to the period T4, is a fourth read out periodof the dynamic range expansion signal of the n-th row.

The period T11, similarly to the period T5, is a reset period of afourth read out of the reset signal and the floating diffusion region FDof the n-th row. The signal ΦRES_n becomes a high level, and thetransistor RES of the n-th row is turned on. As a result, the floatingdiffusion region FD is reset. Next, the signal ΦRES_n becomes a lowlevel, and the transistor RES of the n-th row is turned off. By makingthe signal ΦSEL_n a high level from a low level, the source followertransistor SF reads out the signal based on the potential of thefloating diffusion region FD as a reset signal (noise signal). Thecolumn signal processing circuit 102 a or 102 b reads out the resetsignal and holds it. The read out amplifier 105 a or 105 b subtracts thereset signal from the dynamic range expansion signal, so that the pixelsignal reduced in noise is output.

The period T12 is a first read out period of the photo diode signal ofthe n-th row. The signal ΦTX_n becomes a high level, and the transfertransistor TX of the n-th row is turned on. The carrier accumulated inthe photo diode PD is output to the floating diffusion region FD. Bymaking the signal ΦSEL_n a high level from a low level, the sourcefollower transistor SF reads out the signal based on the potential ofthe floating diffusion region FD as a photo diode signal. The columnsignal processing circuit 102 a or 102 b reads out the photo diodesignal and holds it.

The period T13, similarly to the period T7, is a fourth read out periodof the dynamic range expansion signal of the (n+1)th row.

The period T14 is a period for a fourth read out of the reset signal anda reset of the floating diffusion FD of the (n+1)th row. The signalΦRES_n+1 becomes a high level, and the transistor RES of the (n+1)th rowis turned on. As a result, the floating diffusion region FD is reset.Next, the signal ΦRES_n+1 becomes a low level, and the transistor RES ofthe (n+1)th row is turned off. By making the signal ΦRES_n a high levelfrom a low level, the source follower transistor SF reads out the signalbased on the potential of the floating diffusion region FD as a resetsignal (noise signal). The column signal processing circuit 102 a or 102b reads out the reset signal and holds it. The read out amplifier 105 aor 105 b subtracts the reset signal from the dynamic range expansionsignal, so that the pixel signal reduced in noise is output.

The period T15 is a first read out period of the photo diode signal ofthe (n+1)th row. The signal ΦTX_n+1 becomes a high level, and thetransfer transistor TX of the (n+1)th row is turned on. The carrieraccumulated in the photo diode PD is output to the floating diffusionregion FD. By making the signal ΦSEL_n a high level from a low level,the source follower transistor SF reads out the signal based on thepotential of the floating diffusion region FD as a photo diode signal.The column signal processing circuit 102 a or 102 b reads out the photodiode signal and holds it.

Next, the processings of the fourth read out period of the dynamic rangeexpansion signal of the (n+2)th row, the fourth read out of the resetsignal of the (n+2)th row and the reset period of the floating diffusionFD, and the first readout period of the photo diode signal of the(n+2)th row are performed. These processings are the same as those ofthe periods T10, T11, and T12.

The driving condition of the solid-state imaging apparatus of thepresent embodiment has used an apparatus whose read out time of all thepixels takes approximately 30 milliseconds. As against one second of theaccumulation time of the photo diode PD, the dynamic range expansionsignal reads out the pixel approximately every 250 seconds by dividingit in four times. That is, in the accumulation time longer than thereading time of one frame, the read out operation is performed bydividing the signal overflowed in the same accumulation period in pluraltimes, and the reset operation of the signal overflowed after each readout operation is performed.

The read out operation in the present embodiment is an operation ofreading out the signal based on the carrier, which is generated in thephoto diode by conducting the SEL switch, to the column signalprocessing circuit. Further, the subtracting process of the reset signalcan be performed in a clamp circuit and the like in which the columnsignal processing circuits 102 a and 102 b are provided.

By so doing, by the dark current generated on the floating diffusionregion FD and the holding capacitor Ccs, the dynamic range expansionsignal can be prevented from being suppressed. Specifically, voltageamplitude at the floating diffusion region FD and the holding capacitorCcs was 0.5 V at the maximum, whereas the signal by the dark current wasgenerated approximately 100 mV. However, by reading out this signal bydividing it in four times, the voltage was suppressed to 25 mV per onereading time. This signal readout in four divided times is added everypixel by a processing circuit 803 different from the solid-state imagingapparatus, so that the dynamic range is also expanded by that much.Needless to say, a processing circuit may be provided inside thesolid-state imaging apparatus, so that the addition is performed insidethe solid-state imaging apparatus.

That is, in the method of Japanese Patent Application Laid-Open No.2005-328493, an enlarged amount of the dynamic range was +400 mV, whichis the voltage on the floating diffusion region FD as against asaturation voltage of the photo diode PD. In contrast to this, in thepresent embodiment, it was possible to obtain an enlarged amount of(500−25)×4=1900 mV, which is as much as approximately five times that ofthe dynamic range.

The above described value of the dark current is a value of the averagepixel. Similarly as the photo diode PD having a white spot (white flaw),the floating diffusion region FD and the holding capacitor Ccs have alsothe flaws, and depending on the pixels, there are some that have thedark current as much as 100 times that of the average pixel. In such apixel, the dynamic range expansion signal of +400 mV is not obtained,and in some cases, it is hardly not held. In the present embodiment,there is an effect of not only expanding the dynamic range of theaverage pixel, but also reducing or eliminating the pixel that is unableto hold the dynamic range expansion signal as described above.

The important thing is that the dark current is also reset in order toperform the reset operation after reading out the dynamic rangeexpansion signal. Further, by reading out and processing the dynamicrange expansion signal of the approximately same period as theaccumulation period of the photo diode PD, the synchronicity of bothsignals can be secured.

The reason why “the approximately the same period” is referred to hereis because information during the read out period is not obtained in aprecise sense. That is, as against several hundreds milliseconds toseveral tens seconds of the overall accumulation period, the read outtime is approximately ten μ seconds, and it is 10 μsecond×the number ofread out times and approximately 1/10000 when the information ismissing. Each dynamic range expansion signal may be simply added or thegain may be multiplied and added. Further, the gain may be weighted andadded or may be added after partially adding the compensationprocessing. In whichever method employed, it is important that thesignal information in the same accumulation period is included. Thesynchronicity is extremely important item when the image of a longtime-second still image such as a firework in particular is handled.

Instead of FIG. 3, the driving of FIG. 10 may be performed. FIG. 10 isdifferent from FIG. 3 in that the pulses of the signals ΦSEL_n,ΦSEL_n+1, and ΦSEL_n+2 are not changed at the selection time.

FIG. 4 is a view showing the photoelectric conversion characteristics ofthe present embodiment, and shows an output signal from a sensor chip100. A characteristic Aa is a signal of the photo diode PD.Characteristics Ab, Ac, Ad, and Ae are the read out signals from thefirst to the fourth dynamic range expansion signals. At this time, thereason why the inclination of the characteristic Aa and the inclinationof the characteristic Ab are different is because the dynamic rangeexpansion signal is converted into voltage by the capacitance of sum ofthe capacitance of the floating diffusion region FD and the holdingcapacitor Ccs. Further, a characteristic Af is an output voltage on thefloating diffusion region FD and the holding capacitor Ccs by the darkcurrent on the floating diffusion region FD and the holding capacitorCcs in Japanese Patent Application Laid-Open No. 2005-328493. Acharacteristic Ag is an output voltage on the floating diffusion regionFD and the holding capacitor Ccs by the dark current on the floatingdiffusion region FD and the holding capacitor Ccs in the presentembodiment.

In Japanese Patent Application Laid-Open No. 2005-328493, the dynamicrange expansion amount is VD. In the present embodiment, when a VDR isused, the dynamic range expansion amount is expressed in the followingformula.

[the number of read out times]×VDR×{[capacitance of FD]+[capacitance ofCcs]}/[capacitance of FD]

Consequently, according to the number of read out times, the dynamicrange expansion amount can be increased.

Second Embodiment

FIG. 5 is a timing chart showing a drive timing of a solid-state imagingapparatus according to a second embodiment of the present invention. Thepresent embodiment is driven by the timing shown in FIG. 5 in the samecircuit as the first embodiment. FIG. 5 is the drive timing chart inpixel units from the n-th row to the (n+2)th row of the presentembodiment. The present embodiment (FIG. 5) is different from the firstembodiment (FIG. 3) in that a signal ΦSW is fixed at a high level duringthe carrier accumulation period of a photo diode PD. By operating insuch a manner, the operations of the period T6 and the like which werethe first embodiment are not required. That is, at the period T6 and thelike, the signal ΦRES is not required to be made high level. Similarlyto the first embodiment, the signals ΦSEL_n, ΦSEL_n+1, and ΦSEL_n+2 ofFIG. 10 may be applied.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIGS. 6 and 7.

FIG. 6 is a circuit diagram showing a configuration example of a pixelunit inside a photo receiving region 101 of FIG. 2. The presentembodiment (FIG. 6) is different from the first embodiment (FIG. 1) inthat there is neither holding capacitor Ccs nor transistor SW. The drivetiming of the present embodiment is the same as the one excluding thesignal ΦSW from among the drive timings of FIG. 5. Even when there is noholding capacitor Ccs, the effect of the present embodiment is the sameas that of the first embodiment. In a carrier accumulation period of aphoto diode PD, a transfer switch TX is turned off, and when a carrieris overflowed from the accumulation unit of the photo diode PD, theoverflowed carrier flows to a floating diffusion region FD through atransfer switch TX.

FIG. 7 is a view showing the photoelectric conversion characteristics ofthe solid-state imaging apparatus. In the photoelectric conversioncharacteristics, characteristics Aa to Ag indicate the samecharacteristics of the first embodiment (FIG. 4). The reason why theinclinations of the characteristics Aa and Ab are equal is because bothof the signal of the photo diode PD and the dynamic range expansionsignal are converted into voltage by the capacitance of the floatingdiffusion region FD. If such a form is taken, subsequently, when theaddition is performed suitably by a processing circuit, the processingbecomes simple, and a system load is reduced, and the processing timebecomes high speed.

The characteristic of the present embodiment is that the number ofpixels within one pixel unit is few, and the embodiment can also copewith the pixel unit which is much smaller in size. Although theexpansion amount of the dynamic range is few, the amount can besupplemented by increasing the number of read out times.

Further, the present embodiment is provided with an overflow drain fordischarging the carrier overflowed in a route different from thetransfer switch TX to the photo diode PD, so that the expansion amountof the dynamic range can be further increased. Even in this case, thesame effect can be obtained. The photoelectric conversion characteristicin this case becomes as shown in FIG. 4, and a difference in theinclinations of the characteristics Aa and Ab has the followingrelationship.

Assuming that a carrier amount overflowed from the photo diode PD=A, acarrier amount discharged by the overflow drain=B, a carrier amount heldin the floating diffusion region FD=C, an inclination of thecharacteristic Aa=α, and an inclination of the characteristic Ab=β, thefollowing relationship is established.

A=B+C

α/β=A/C

By providing the overflow drain, the dynamic range can be furtherexpanded.

Further, as a modification of the present embodiment, a Ccs unit isprovided, and this Ccs unit is composed of a PN junction capacitanceonly and can be considered also to have a configuration not providedwith a capacitance by a gate oxide film. The Ccs unit has a PN junctioncapacitor composed of a semiconductor substrate and a high densityimpurity region.

Fourth Embodiment

With reference to FIG. 8, a fourth embodiment of the present inventionwill be described. FIG. 8 is a view showing a configuration example of acamera system in a case when a solid-state imaging apparatus accordingto a fourth embodiment of the present invention is used for a camera. Asensor 802 in the figure corresponds to a sensor chip 100 of FIG. 2, andthe solid-state imaging apparatus according to the third embodiment wasused. Needless to say, it does not matter if the solid-state imagingapparatus according to other embodiments are used. The signals outputfrom a sensor 802, that is, a dynamic range expansion signal and a photodiode signal are held in a memory 804 through a processing circuit 803.The processing circuit 803 uses the memory 804 to add and process thedynamic range expansion signal and the photo diode signal. After thecompletion of carrier accumulation, the last photo diode signal is readout from the sensor 802 to the processing circuit 803. The processingcircuit 803 outputs the added and processed signals to an imageprocessing circuit 805. The image processing circuit 805 performs animage processing. A timing generator 801 generates control signals ofthe sensor 802, the processing circuit 803, and the memory 804.

In the third embodiment, similarly to FIG. 7, by making thephotoelectric conversion characteristic such that the inclination of thephotoelectric conversion characteristic Aa before saturation and theinclinations of the photoelectric conversion characteristics Ab to Aeafter saturation are equal, the processing circuit 803 has only toperform a simple addition processing, so that the processing circuit 803can be made simple.

Fifth Embodiment

FIG. 9 is a timing chart showing a drive timing of a solid-state imagingapparatus according to a fifth embodiment of the present invention. Thepresent embodiment is an embodiment in a case of using a mechanicalshutter together, and uses the same circuit as that of the firstembodiment. At the time t1, the mechanical shutter is opened, and at thetime t3, the mechanical shutter is closed. The operations of periods T1to T15 are the same as those of FIG. 5 provided that the operations ofthe periods T1 to T3 are simultaneously performed.

A start of exposure is regulated by the mechanical shutter open of thetime t1, and an end of exposure is regulated by the mechanical shutterclose of the time t3. Since the start of exposure is regulated by themechanical shutter, similarly to the first embodiment, even when resetoperations of the periods T1 to T3 are sequentially performed, when themechanical shutter is opened after the end of resetting all the rows,the same image can be obtained. Further, when the mechanical shutter isclosed at the time t2, the last dynamic range expansion signal containsthe dark current information only of the floating diffusion region FD.Hence, the front-half three signals are added, and the last signal issubtracted, so that the fixed pattern noise can be also reduced.

The drive timing when using the mechanical shutter together is not theone limited to FIG. 9, and even by the driving timings of FIGS. 3 and 5,if the mechanical shutter is worked together based on the abovedescribed idea, a good image can be obtained. Further, similarly to thefirst embodiment, the signals ΦSEL_n, ΦSEL_n+1, and ΦSEL_n+2 of FIG. 10may be applied.

As described above, the first to the fifth embodiments are thesolid-state imaging apparatus two-dimensionally disposed with the pixelunit composed of at least a photo diode PD and a transfer switch TX fortransferring the signal of the photo diode PD, and a holding capacitorCcs for holding the signal overflowed from the photo diode PD. Theapparatus reads out the signal overflowed in the same accumulationperiod by dividing it in plural times, and performs a reset operation ofthe overflowed signal after each reading.

Japanese Patent Application Laid-Open No. 2005-328493 discloses one timereading only of the dynamic range expansion signal for the carrieraccumulation period of the photo diode. That is, in Japanese PatentApplication Laid-Open No. 2005-328493, as against one time reading ofthe photo diode, the read out of the dynamic range expansion signal isone time only. The present embodiment reads out the dynamic rangeexpansion signal plural times for the carrier accumulation period of thephoto diode PD, and secures the synchronicity of the carrieraccumulation periods of the photo diode PD and the holding capacitorCcs, while making it possible to expand the dynamic range.

In the solid-state imaging apparatus of the first to the fifthembodiments, the photo diode PD is a photoelectric conversion unit forgenerating the carrier by the photoelectric conversion and accumulatingthe generated carrier. The holding capacitor Ccs or the floatingdiffusion region FD is a carrier accumulation unit for accumulating acarrier overflowed from the photoelectric conversion unit PD. A rowselection switch SEL is a read out unit for reading out the signal basedon the carrier generated in the photoelectric conversion unit to theoutside. This read out unit may contain a vertical scanning circuit 104for driving the row selection switch SEL. The column signal processingcircuits 102 a and 102 b read out the signal based on the carrieraccumulated in the carrier accumulating unit Ccs or the FD in thecarrier accumulation period of one time with respect to the carriergenerated by the photoelectric conversion unit PD, and processes thissignal. A reset switch RES resets the carrier accumulated in the carrieraccumulation unit Ccs or the FD after each reading of the read out units102 a and 102 b.

In the first embodiment (FIG. 1), the carrier accumulation unit is theholding capacitor Ccs. The transfer switch TX is a switch fortransferring the carrier accumulated in the photoelectric conversionunit PD to the floating diffusion region FD. A switch SW is connectionswitch for connecting between the carrier accumulation unit Ccs and thefloating diffusion region FD. This switch reads out the signal based onthe carrier of the floating diffusion region FD through a sourcefollower transistor SF by the control of a row selection switch SEL.

In the third embodiment (FIG. 6), the carrier accumulation unit is afloating diffusion region FD. The switch TX is a transfer switch fortransferring the carrier accumulated in the photoelectric conversionunit PD to the floating diffusion region FD. This switch reads out thesignal based on the carrier of the floating diffusion region FD by thecontrol of the row selection switch SEL.

The read out units 102 a and 102 b read out the carrier accumulated inthe photoelectric conversion unit PD after reading the carrieraccumulated in the carrier accumulation unit Ccs or the FD plural timesin the first carrier accumulation period.

The above described embodiments have been described only in thepreferred forms, respectively, and are to be considered in all aspectsas illustrative and not restrictive. That is, the present invention maybe embodied in various forms without departing from the spirit oressential characteristics thereof.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-176510, filed Jul. 4, 2007, which is hereby incorporated byreference herein in its entirety.

1. An imaging apparatus comprising: a photoelectric conversion unit forgenerating a carrier by a photoelectric conversion, and for accumulatingthe carrier generated; a transfer switch for transferring the carrierfrom the photoelectric conversion unit; a carrier accumulation unit foraccumulating the carrier overflowed from the photoelectric conversionunit; a read out unit for reading out, at plural times, a signal basedon the carrier accumulated in the carrier accumulation unit during asingle carrier accumulation time period for the carrier generated by thephotoelectric conversion unit; and a reset switch for resetting thecarrier accumulated in the carrier accumulation unit after each time ofthe read out by the read out unit, wherein during the plural times ofthe read out, the transfer switch is not turned on.
 2. The imagingapparatus according to claim 1, wherein the transfer switch transfersthe carrier accumulated in the photoelectric conversion unit to afloating diffusion region, a connection switch is provided forconnecting between the carrier accumulation unit and the floatingdiffusion region, and the read out unit reads out a signal based on thecarrier in the floating diffusion region.
 3. The imaging apparatusaccording to claim 1, wherein the carrier accumulation unit is afloating diffusion region, the transfer switch transfers the carrieraccumulated in the photoelectric conversion unit to the floatingdiffusion region, and the read out unit reads out a signal based on thecarrier in the floating diffusion region.
 4. The imaging apparatusaccording to claim 1, wherein the read out unit reads out a signal basedon the carrier accumulated in the photoelectric conversion unit, afterthe plural times of reading out the signal based on the carrieraccumulated in the carrier accumulation unit during the single carrieraccumulation time period.
 5. The imaging apparatus according to claim 1,wherein the carrier accumulation unit has PN junction capacitor.
 6. Theimaging apparatus according to claim 1, wherein the read out unit readsout the signal, at the plural times, for a accumulation period longerthan a one frame reading out period, and the reset switch performs theresetting.
 7. A processing method of an imaging apparatus comprising: aphotoelectric conversion unit for generating a carrier by aphotoelectric conversion, and for accumulating the carrier generated;and a transfer switch for transferring the carrier form thephotoelectric conversion unit; a carrier accumulation unit foraccumulating the carrier overflowed from the photoelectric conversionunit, wherein the method comprises steps of: reading out, at pluraltimes, a signal based on the carrier accumulated in the carrieraccumulation unit during a single carrier accumulation time period forthe carrier generated by the photoelectric conversion unit; andresetting the carrier accumulated in the carrier accumulation unit aftereach time of the read out by the read out unit, wherein the plural timesof the reading out is performed without turning on the transfer switch.